1. Field of the Invention
This invention related generally to waveguides and devices for interconnecting waveguides, and, more particularly, to a waveguide seal which provides reliable contact between the seal and the waveguides interconnected with the seal and which provides an insulating gap between flanges of the mating waveguides and the seal to better control the electric field.
2. Discussion
A waveguide may generally be described as a device which constrains or guides the propagation of electromagnetic waves along a path defined by the physical construction of the waveguide. The term waveguide usually refers to a metallic tube which confines and guides the propagation of electromagnetic waves in the hollow space along the lengthwise direction of the tube.
When waveguide systems are assembled, smaller lengths of waveguides are typically interconnected to provide a waveguide of sufficient length. Preferably, the interconnection of the waveguides provides a joint that will transmit high power across the joint with no electrical arcing and also provides an efficient radio frequency (RF) seal having little or no loss of signal strength.
Many factors impact the waveguide power handling ability, which impacts the waveguide capacity. For example, because sufficient mechanical contact between the waveguides is difficult to achieve, small gaps often appear between the mating waveguides. These small gaps reduce the electrical power handling capacity of the waveguide by causing large shunt electric (E) field breakdown.
More particularly, reliable contact between the mating flanges of the waveguides to eliminate gaps is most importantly achieved along the inside mating surfaces and corners to accommodate the skin depth of the current along the inner surface of the waveguide. If contact is not properly made, electric field strengths build and reduce the power handling capacity of the waveguides. Small imperfections in the waveguide surfaces prevent the inside corners from properly touching. In order to reduce the electric field, large gaps may be used to provide better power handling by the waveguide. However, the large gaps cause reflection in the flow of energy and enable energy to escape the waveguide.
From the foregoing, it becomes readily apparent that the interconnection of waveguides becomes an integral part of the proper operation and acceptable reliability of the waveguide system. There are various types of joints which are typically used to connect waveguides. A first joint, and generally the simplest, comprises a contact coupling mating two opposing flanges of the waveguide. Contact couplings do not generally consider power handling capabilities. Thus, a minor misalignment, a warped flange, or various surface imperfections result in arcing at the joint.
A second type of joint is characterized as a choke flange. Choke flanges insert large gaps between the mating waveguides in order to reduce arcing. The gap is preferably sized to reduce the electric field in order to minimize or eliminate breakdown. Typically, the gap extends as a shunt 1/2 wavelength transmission line circuit. The transmission line is short circuited in a cavity, thus lowering the reflection and electromagnetic interference (EMI) caused by the large gap or perturbation. However, choke circuits require relatively substantial volume to form such a distributed transmission line matching network.
A third type of joint may be formed by placing a gasket-type seal between the waveguide flanges. The seal typically provides reliable contact without gaps by compressing a conducting relief surface into each of the mating flanges. The joining surface may be milled with a transverse ridge, a diamond knurl, or diecast with some type of regular roughness. Although the gasket-type seal provides reliable electrical connection between the seal and the flanges, the gasket-type seal typically abrades the smooth flange surface while being compressed during assembly. The gasket-type seal results in a destructive union between the waveguides and is typically avoided in assemblies where the flange surfaces may be disassembled, then reassembled.
A flange joint can become an extremely important component in any waveguide system. Many microwave systems include flange joints. If arcing occurs in the flange joint, the joint may degrade or totally disrupt the overall performance of the system. Repairing flange joints typically includes disassembling the joint and replacing the waveguide flanges or seals. Such repair may be costly and difficult to effectuate in remotely located systems. More specifically, waveguide arcing may be a particularly important issue in high power microwave systems. Examples of radar systems using such flange joints include surface radar which uses high power waveguide flanges, airborne and spacecraft radar, satellite earth stations or up link, microwave relays, industrial ovens, and automobile radar as well.
Thus, it is an object of the present invention to join two waveguides at a joint while minimizing power handling capabilities at the joint.
It is a further object of the present invention to join two waveguides at a joint which transfers electromagnetic energy without electrical breakdown.
It is a further object of the present invention to provide a waveguide seal in which the gaps between the seal and the mating waveguide sections are arranged in order to control the electric field in proximity to the joint.
It is yet a further object of this invention to provide a waveguide seal in which the electric field in proximity to the seal is lower than the breakdown condition.
It is yet a further object of this invention to provide a seal for joining two waveguides at a joint, where the seal provides reliable mechanical contact between the two waveguides.
It is yet a further object of the present invention to join two waveguides using a seal which compensates for imperfections in the waveguides to provide reliable mechanical and electrical contact.
It is yet a further object of this invention to join two waveguides using an RF seal at a joint having high power capabilities, low loss, environmental sealing capabilities, and small volume.
It is yet a further object of this invention to provide a seal for joining two waveguides at a joint, where the seal interconnects two waveguides having relatively narrow flanges.
It is yet a further object of this invention to provide a seal for joining two waveguides at a joint, where the seal interconnections two waveguides using a minimum of fasteners.